Chapter 4 Evolution, Biological Communities and Species Interactions

Chapter 4 textbook Powerpoint chapt04_lecture.pdf

4.1 Evolution

Allopatric and Sympatric Speciation

Allopatric- In allopatric speciation, new species are created when members of one original species are geographically isolated. They begin to develop new traits, which are passed down because they do not breed with the original species.

Sympatric- When new species arise from a common ancestor because of a genetic variation and behavioral barriers that isolate the organism’s reproduction, though they are in the same location as the original species.

Resource Partitioning vs. Niche Specialist

• Partitioning can allow several species to utilize different parts of the same resource and coexist within a habitat
  • Species specialize over time in order to gain access to the resources they need. This is one way to reduce competition because different species share resources. Therefore more species can survive.

• Niche specialists have narrow ecological niches and very specific needs in terms of resources and habitats. They don’t compete as much as other species because they don’t require the same resources as them.

• Partitioning can cause species to specialize in the area of the habitat where they find resources and the type of resources that they rely on. This can cause species to evolve in such a way that they become niche specialists, and are less resilient to environmental changes.

A niche specialist is an extreme example of resource partitioning.

Directional Selection - Certain genes or traits are distributed mroe than others in a population. Many birds have mutations of their beak but mosty mutation result in one general shape/size.
Stabilizing Selection - Less genetic variation within a population. Birds of a population lose a trait all together (short legs).
Disruptive Sleection - One trait will be distibuted to the extreme. Birds gain extremelty long wing spans or relaly short wing spans.

Competitive exclusion	BOTH	Resource partitioning
No two species can occupy the same niche	Process of niche evolution	Several species can use the same resource but different parts of it
More efficient one in using available resources excludes the other	Diversity depends on niches	Can coexist in the same habitat
One species per niche	Genetic variation depends on competition	Multiple species per niche = more diversity
More competition = “fittest” passes down best genes to offspring		Less competition = less genetic variation
No time for production because busy competing, but more genetic variation because they push each other to evolve more		More time to reproduce the same species when less competition

4.2 Relationships

• barnacle ws: competition.pdf
• snake hawk relationships ws:analyzing relationships.pdf
• reading and question ws: brood parasitism article.pdf
• Lynx Hare Ws: what goes up must come down.pdf
• Sea otter, Kelp, Orca --> Which is the keystone in this community - or is there a keystone set of organisms?
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4.3 Properties of Communities

• Community Structure

Pond

Stream

Swamp

• || Species complexity || || || ||
• || Resilience || || || ||
• || Stability || || || ||
• || Edge effect || || || ||
• || ecotones || || || ||

4.4 Community Change

• Primary succession WS: primary succession.pdf
• Secondary Succession WS: secondary succession.pdf
• Aquatic succession WS: succession in a water community.pdf